The present invention relates to viscous couplings, and more particularly, to such couplings employed in automatic transmission torque converters, to serve as bypass elements to bypass the torque converter.
Torque converter type automatic transmissions have achieved widespread application and acceptance in motor vehicles. Although generally satisfactory in this application, torque converter type automatic transmissions inherently involve a certain amount of slippage, and therefore, inherently result in losses in vehicle fuel economy. In an effort to minimize such slippage, and thereby increase fuel economy, efforts have been made to bypass the torque converter with some type of direct drive, which typically is activated when the vehicle is operating in the higher gear ratios, and above a predetermined vehicle speed.
While these prior art direct drive bypass arrangements have resulted in improvements in fuel economy, certain types of bypass element have, under certain operating conditions, transmitted various drive line vibrations to the passenger compartment of the motor vehicle, causing degradation of the ride quality of the vehicle.
In an effort to provide a bypass element which would not transmit drive line vibration to the passenger compartment, those skilled in the art have utilized a viscous coupling as the bypass element. Although the use of a viscous coupling as the bypass element does serve to minimize transmission of drive line vibrations to the passenger compartment, it is important that the coupling be designed for maximum efficiency and maximum durability.
One of the concerns associated with the use of a viscous coupling as a bypass element in a torque converter of an automatic transmission is the possibility of the automatic transmission fluid leaking into the viscous fluid in the viscous coupling, or visa versa. The result has been that the viscous couplings utilized commercially have included extremely complex and expensive sealing arrangements. The sealing arrangement which has been in use commercially by the assignee of the present invention is illustrated in U.S. Pat. No. 4,462,492, assigned to the assignee of the present invention and incorporated herein by reference. The prior art sealing arrangement has included double-lip seals which are expensive, and the associated structure on which the seals are seated results in complex and expensive machining operations.